AMDGPU/GlobalISel: Select G_CTTZ_ZERO_UNDEF

Directly select this rather than going through the intermediate
instruction, which may provide some combine value in the future.

Author: arsenm

llvm/lib/Target/AMDGPU/AMDGPUInstrInfo.td

@@ -286,7 +286,7 @@ def AMDGPUbfm : SDNode<"AMDGPUISD::BFM", SDTIntBinOp>;
 def AMDGPUffbh_u32_impl : SDNode<"AMDGPUISD::FFBH_U32", SDTIntBitCountUnaryOp>;
 def AMDGPUffbh_i32_impl : SDNode<"AMDGPUISD::FFBH_I32", SDTIntBitCountUnaryOp>;
 
-def AMDGPUffbl_b32 : SDNode<"AMDGPUISD::FFBL_B32", SDTIntUnaryOp>;
+def AMDGPUffbl_b32_impl : SDNode<"AMDGPUISD::FFBL_B32", SDTIntBitCountUnaryOp>;
 
 // Signed and unsigned 24-bit multiply. The highest 8-bits are ignore
 // when performing the mulitply. The result is a 32-bit value.
@@ -425,6 +425,10 @@ def AMDGPUffbh_u32 : PatFrags<(ops node:$src),
   [(ctlz_zero_undef node:$src),
    (AMDGPUffbh_u32_impl node:$src)]>;
 
+def AMDGPUffbl_b32 : PatFrags<(ops node:$src),
+  [(cttz_zero_undef node:$src),
+   (AMDGPUffbl_b32_impl node:$src)]>;
+
 def AMDGPUpkrtz_f16_f32 : PatFrags<(ops node:$src0, node:$src1),
   [(int_amdgcn_cvt_pkrtz node:$src0, node:$src1),
   (AMDGPUpkrtz_f16_f32_impl node:$src0, node:$src1)]>;

llvm/lib/Target/AMDGPU/SOPInstructions.td

@@ -210,7 +210,9 @@ def S_BCNT1_I32_B64 : SOP1_32_64 <"s_bcnt1_i32_b64",
 
 def S_FF0_I32_B32 : SOP1_32 <"s_ff0_i32_b32">;
 def S_FF0_I32_B64 : SOP1_32_64 <"s_ff0_i32_b64">;
-def S_FF1_I32_B64 : SOP1_32_64 <"s_ff1_i32_b64">;
+def S_FF1_I32_B64 : SOP1_32_64 <"s_ff1_i32_b64",
+  [(set i32:$sdst, (AMDGPUffbl_b32 i64:$src0))]
+>;
 
 def S_FF1_I32_B32 : SOP1_32 <"s_ff1_i32_b32",
   [(set i32:$sdst, (AMDGPUffbl_b32 i32:$src0))]

llvm/lib/Target/AMDGPU/VOP1Instructions.td

@@ -241,7 +241,7 @@ defm V_COS_F32 : VOP1Inst <"v_cos_f32", VOP_F32_F32, AMDGPUcos>;
 defm V_NOT_B32 : VOP1Inst <"v_not_b32", VOP_I32_I32>;
 defm V_BFREV_B32 : VOP1Inst <"v_bfrev_b32", VOP_I32_I32, bitreverse>;
 defm V_FFBH_U32 : VOP1Inst <"v_ffbh_u32", VOP_I32_I32, AMDGPUffbh_u32>;
-defm V_FFBL_B32 : VOP1Inst <"v_ffbl_b32", VOP_I32_I32>;
+defm V_FFBL_B32 : VOP1Inst <"v_ffbl_b32", VOP_I32_I32, AMDGPUffbl_b32>;
 defm V_FFBH_I32 : VOP1Inst <"v_ffbh_i32", VOP_I32_I32, AMDGPUffbh_i32>;
 
 let SchedRW = [WriteDoubleAdd] in {

llvm/test/CodeGen/AMDGPU/GlobalISel/inst-select-cttz-zero-undef.mir

@@ -0,0 +1,82 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -march=amdgcn -mcpu=tahiti -run-pass=instruction-select -verify-machineinstrs %s -o - | FileCheck %s
+
+---
+name: cttz_zero_undef_s32_ss
+legalized: true
+regBankSelected: true
+tracksRegLiveness: true
+
+body: |
+  bb.0:
+    liveins: $sgpr0
+
+    ; CHECK-LABEL: name: cttz_zero_undef_s32_ss
+    ; CHECK: liveins: $sgpr0
+    ; CHECK: [[COPY:%[0-9]+]]:sreg_32 = COPY $sgpr0
+    ; CHECK: [[S_FF1_I32_B32_:%[0-9]+]]:sreg_32 = S_FF1_I32_B32 [[COPY]]
+    ; CHECK: S_ENDPGM 0, implicit [[S_FF1_I32_B32_]]
+    %0:sgpr(s32) = COPY $sgpr0
+    %1:sgpr(s32) = G_CTTZ_ZERO_UNDEF %0
+    S_ENDPGM 0, implicit %1
+...
+
+---
+name: cttz_zero_undef_s32_vs
+legalized: true
+regBankSelected: true
+tracksRegLiveness: true
+
+body: |
+  bb.0:
+    liveins: $sgpr0
+
+    ; CHECK-LABEL: name: cttz_zero_undef_s32_vs
+    ; CHECK: liveins: $sgpr0
+    ; CHECK: [[COPY:%[0-9]+]]:sreg_32 = COPY $sgpr0
+    ; CHECK: [[V_FFBL_B32_e64_:%[0-9]+]]:vgpr_32 = V_FFBL_B32_e64 [[COPY]], implicit $exec
+    ; CHECK: S_ENDPGM 0, implicit [[V_FFBL_B32_e64_]]
+    %0:sgpr(s32) = COPY $sgpr0
+    %1:vgpr(s32) = G_CTTZ_ZERO_UNDEF %0
+    S_ENDPGM 0, implicit %1
+...
+
+---
+name: cttz_zero_undef_s32_vv
+legalized: true
+regBankSelected: true
+tracksRegLiveness: true
+
+body: |
+  bb.0:
+    liveins: $vgpr0
+
+    ; CHECK-LABEL: name: cttz_zero_undef_s32_vv
+    ; CHECK: liveins: $vgpr0
+    ; CHECK: [[COPY:%[0-9]+]]:vgpr_32 = COPY $vgpr0
+    ; CHECK: [[V_FFBL_B32_e64_:%[0-9]+]]:vgpr_32 = V_FFBL_B32_e64 [[COPY]], implicit $exec
+    ; CHECK: S_ENDPGM 0, implicit [[V_FFBL_B32_e64_]]
+    %0:vgpr(s32) = COPY $vgpr0
+    %1:vgpr(s32) = G_CTTZ_ZERO_UNDEF %0
+    S_ENDPGM 0, implicit %1
+...
+
+---
+name: cttz_zero_undef_s64_ss
+legalized: true
+regBankSelected: true
+tracksRegLiveness: true
+
+body: |
+  bb.0:
+    liveins: $sgpr0_sgpr1
+
+    ; CHECK-LABEL: name: cttz_zero_undef_s64_ss
+    ; CHECK: liveins: $sgpr0_sgpr1
+    ; CHECK: [[COPY:%[0-9]+]]:sreg_64 = COPY $sgpr0_sgpr1
+    ; CHECK: [[S_FF1_I32_B64_:%[0-9]+]]:sreg_32 = S_FF1_I32_B64 [[COPY]]
+    ; CHECK: S_ENDPGM 0, implicit [[S_FF1_I32_B64_]]
+    %0:sgpr(s64) = COPY $sgpr0_sgpr1
+    %1:sgpr(s32) = G_CTTZ_ZERO_UNDEF %0
+    S_ENDPGM 0, implicit %1
+...